I believe this actually came from a collection made by Marjory Kennedy Fraser late in the 19th century. Songs of the Hebrides, The Sea Tangle, etc Gordon's aunt used to sing these songs to him. Incredible melody
Gordon wrote the last verse.
I am told by friend on Skye that the traditional pronounciation is Room- it has bee "anglicized to Rum

here is how I learned it from him

Far away seaward my green land, my youth land
Far away seaward the cuillins of Rhum
At night on the dreamtide I'm hearing hill waters
And laughter of streams at the cuillins of Rhum

Far on the dreamtrack thy green hills are lovelit
Where ride the hill waters down to the sea
They tumble at noontide like snow wreath in moonlight
As those who are yearning would yearn it to be

When shall I see your bold shores in the sunlight
The heather of hills at the rising of morn
The blowing grey sea wind goes east in the morning
To run the wild hills of the cuillins of Rhum